Any time you are planning to make multiple pieces of the same design it is wise to write out a list of the parts and the sizes of those parts in addition to making a diagram with dimensions of the completed piece. I make candleholders, wall sconces and wine racks with a few other items thrown in for good measure. I started keeping a plans book almost immediately on deciding to do production work. It has served me well.
I made a mistake last week. I consulted my plans book for sizes on a particular piece and started knocking out the parts for three copies. My mistake was in not realizing how long it had been since I made the last one of these candle holders. I also had failed to note a change in materials which ended up costing me most of two days work and twenty feet of stock. It was only a small change but it caused one thing to go wrong and that caused two things to go wrong and the each caused two other things to go wrong and before I realized it I had a pile of scrap metal instead of three candleholders.
To avoid this sort of thing I suggest keeping your plans book up to date. Any changes you make need to be noted when you make them. Don't wait a day or two and then note them. You run too big of a risk of putting it off until you've forgotten what the changes were or even that you made the changes in the first place. The other thing I suggest is making one component to start with to be sure you can remember the process. That way if you do what I did you won't end up with a mess and a loss of profits. It can also save a good deal of time in the long run even if it feels like you are wasting time.